1. Field of the Invention
The present invention relates to a battery module, and in particular, to a battery module having an improved unit battery assembly coupling structure to minimize volume.
2. Description of the Related Art
A rechargeable battery module typically includes rechargeable batteries (also known as unit cells) connected in series.
The unit cells each include an electrode assembly having positive and negative electrodes and a separator interposed between the positive and negative electrodes, a case for receiving the electrode assembly, a cap assembly for sealing the case, and positive and negative terminals electrically connected to the positive and negative electrodes, respectively.
The unit cells are typically of a cylindrical or prismatic shape. If the unit cell is a prismatic type, the positive and negative terminals protrude out of the cap assembly so that they are exposed to the outside of the unit cell.
In the battery module having the prismatic type unit cells, the unit cells are arranged so as to alternate positive and negative terminals of one unit cell with the positive and negative terminals of an adjacent unit cell. The positive and negative terminals are connected to each other by an electric conductor. The electric conductor is typically fixed on the positive and negative terminals by nuts screw-coupled to the positive and negative terminals.
The battery module is formed by several to tens of unit cells stacked together and electrically connected to each other. In order to fix the stacked unit cells, end plates are disposed on both outermost unit cells among the stacked unit cells. The end plates are typically connected to each other by connecting rods and nuts so as to fix the stacked unit cells by applying pressing force to the stacked unit cells.
However, with the conventional battery module, it is time-consuming to connect the connecting rods to the end plates.
Furthermore, since the connecting rods and the nuts coupled to the connecting rods project to the outside of the stacked unit cells, the volume of the battery module increases. The increase in volume of the battery module, in turn, causes an increase of the volume of a device to which the battery module is typically installed. As such, device designs become limited.
Particularly, when the battery module is used as the power source for driving motors, such as those for hybrid electric vehicles, electric vehicles, electric scooters, electric bicycles, vacuum cleaners, or the like, there is a need to minimize the volume of the battery module considering the limited battery module installing space of the devices.